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Research Questions

How did Medicaid expansion affect insurance status for low-income childless adults who became newly eligible?

Of the newly eligible adults gaining Medicaid coverage because of the expansion, how many would otherwise have been uninsured, and how many would otherwise have been covered by private insurance?

Which subgroups of the newly eligible population were more or less likely to take up Medicaid coverage in 2014?

The authors used the National Health Interview Survey (NHIS) to estimate how the Affordable Care Act Medicaid expansion affected health insurance enrollment, by source of coverage, among childless adults who became newly eligible for Medicaid in 2014. The NHIS data allowed the authors to report changes in enrollment by source of coverage and to conduct subgroup analyses of Medicaid take-up by gender, age, and other characteristics. Newly eligible childless adults in expansion states were 8.9 percentage points more likely to be insured in 2014 relative to similar adults in nonexpansion states, reflecting gains in Medicaid with little to no offsetting decrease in private coverage. Subgroup patterns of take-up among the newly eligible differed from findings previously reported for the wider low-income population, many of whom were previously eligible. Because these estimates isolate the behavior of newly eligible adults, these findings may be useful for anticipating take-up if nonexpansion states with limited Medicaid eligibility under current law choose to expand in the future. Similarly, because the control group excludes adults who became eligible for subsidized insurance coverage through the Health Insurance Marketplace, these findings provide insight into the effects of Medicaid expansion relative to a counterfactual involving neither Medicaid expansion nor Marketplace subsidies.

Key Findings

Overall Coverage Analyses

The results corroborate findings from other data sources that insurance coverage increases were larger in states that expanded Medicaid. These estimates add to the existing literature because the treatment and control groups were more narrowly defined to exclude those previously eligible for Medicaid and those directly affected by other coverage expansions. By focusing on the group most likely to gain Medicaid eligibility (nondisabled low-income childless adults) and on states that implemented the Medicaid expansion in 2014, this study clarifies the important role played by increased Medicaid coverage in previously reported coverage gains.

The authors found very little evidence of differential changes in private coverage between expansion and nonexpansion states. Estimates by insurance type yielded no significant evidence that the Medicaid expansion crowded out private coverage in the first year of the 2014 coverage expansion.

While the authors found substantial increases in Medicaid coverage, take-up over the first year of the 2014 Medicaid expansion was limited relative to the size of the Medicaid-eligible uninsured population.

Subgroup Analyses

Take-up was lower among men (compared with women), Hispanics and members of other racial/ethnic groups (compared with non-Hispanic whites and Blacks), and adults under age 36 (compared with older adults).

Newly eligible adults in fair or poor health were more likely to gain Medicaid coverage than healthier adults.

Heterogeneity across demographic groups in coverage gains and Medicaid take-up among nondisabled childless adults in poverty were often quite different from the patterns observed among all adults, with women and older adults more likely to gain Medicaid coverage than men and younger adults.

This research was funded by the Robert Wood Johnson Foundation (RWJF) through its State Health Access Reform Evaluation (SHARE) initiative and conducted by RAND Health.

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